Heat-sensitive type flow rate detecting element and holder therefor

Abstract

A flow rate detecting element measuring the flow rates of various fluids, particularly the intake air of an internal combustion engine. The flow rate detecting element has a thin film layer including a support film and a protective film on one surface of a flat substrate, a heating resistance section and a comparative resistance section thermosensitive resistor having patterns and located between the support film and the protective film. The flat substrate has a recess which penetrates the flat substrate in the thickness direction thereof and facing the heating resistance section and the comparative resistance section. A fluid flow passage communicates with the recess which faces the comparative resistance section for fluid flow into the recess. Flow rate or velocity of a fluid can be measured accurately using the heating resistance section according to the fluid temperature reported by the comparative resistance section.

What is claimed is:  
     
       1. A thermosensitive flow rate detecting element comprising: 
       a flat substrate having a surface and end wall transverse to the surface;  
       a thin film layer comprising an insulating support film and an insulating protective film on the surface of the flat substrate;  
       a heating resistance section including a thermally sensitive resistor having a pattern and a comparative resistance section including a thermally sensitive resistor having a pattern, the heating resistance section and the comparative resistance section being disposed between the support film and the protective film of the thin film layer;  
       a recess which penetrates the flat substrate in a thickness direction and faces the heating resistance section and the comparative resistance section; and  
       at least one fluid flow passage through which the recess is in fluid communication with one of a surface of the thin film layer facing away from the recess and one of the end wall surfaces of the substrate, wherein the thermosensitive flow rate detecting element measures one of flow rate and velocity of the fluid, using the heating resistance section, according to fluid temperature sensed by the comparative resistance section.  
     
     
       2. The flow rate detecting element according to  claim 1 , having at least two fluid flow passages. 
     
     
       3. The flow rate detecting element according to  claim 1 , wherein at least one fluid flow passage is provided upstream of the comparative resistance section relative to flow direction of the fluid. 
     
     
       4. The flow rate detecting element according to  claim 1 , wherein at least one fluid flow passage is provided downstream of the comparative resistance section relative to flow direction of the fluid. 
     
     
       5. The flow rate detecting element according to  claim 1 , wherein the comparative resistance section and the heating resistance section are disposed on a line crossing flow direction of the fluid. 
     
     
       6. The flow rate detecting element according to  claim 1 , wherein the comparative resistance section and the heating resistance section are disposed on a line perpendicular to flow direction of the fluid. 
     
     
       7. A thermosensitive flow rate detecting element comprising: 
       a flat substrate having opposed first and second surfaces and end wall surfaces transverse to the first and second surfaces;  
       a thin film layer comprising an insulating support film and an insulating protective film on the first surface of the flat substrate;  
       a heating resistance section including a thermally sensitive resistor having a pattern and a comparative resistance section including a thermally sensitive resistor having a pattern, the heating resistance section and the comparative resistance section being disposed between the support film and the protective film of the thin film layer;  
       a recess which penetrates the flat substrate in a thickness direction and faces the heating resistance section and the comparative resistance section; and  
       at least two fluid flow passages through which the recess is in fluid communication with one of a surface of the thin film layer facing away from the recess and one of the end wall surfaces of the substrate, a first of the two fluid flow passages being upstream of the comparative resistance section and a second of the fluid flow passages being downstream of the comparative resistance section, wherein  
       the thermosensitive flow rate detecting element measures one of flow rate and velocity of the fluid, using the heating resistance section, according to fluid temperature sensed by the comparative resistance section, and  
       the first of the fluid flow passages is selected from the group consisting of  
       (i) a first hole which penetrates the thin film layer in a thickness direction so the fluid flows across the thin film layer on upper and lower surfaces of the thin film layer,  
       (ii) at least one groove in the flat substrate and which communicates between a recess wall surface that faces the comparative resistance section and one of the end wall surfaces of the substrates, on the second surface of the flat substrate, and  
       (iii) at least one tubular passage within the flat substrate and which communicates between the recess wall surface facing the comparative resistance section and one of the end wall surfaces of the substrate.  
     
     
       8. The flow rate detecting element according to  claim 7 , wherein the first of the fluid flow passages is the first hole and the second of the fluid flow passages is selected from the group consisting of 
       (i) a second hole which penetrates the thin film layer in the thickness direction so the fluid flows across the thin film layer between the upper surface and the lower surface,  
       (ii) at least one groove in the flat substrate and which communicates between the recess wall surface that faces the comparative resistance section and one of the end wall surfaces of the substrate, on the second surface of the substrate, and  
       (iii) at least one tubular passage within the flat substrate and which communicates between the recess wall surface that faces the comparative resistance section and one of the end wall surfaces of the substrate.  
     
     
       9. The flow rate detecting element according to  claim 8 , wherein the second of the fluid flow passages is the second hole and each hole of the first and second fluid flow passages is a slit in the thin film layer extending transverse to fluid flow direction. 
     
     
       10. The flow rate detecting element according to  claim 9 , wherein the thin film layer is warped, at least in a part of the comparative resistance section, and is convex relative to the second side of the substrate. 
     
     
       11. The flow rate detecting element according to  claim 7 , wherein the first of the fluid flow passages includes the at least one groove, and the second of the fluid flow passages is selected from the group consisting of; 
       (i) a second hole which penetrates the thin film layer in the thickness direction so the fluid flows across the thin film layer on the upper surface and the lower surface,  
       (ii) at least one groove in the flat substrate and which communicates between the recess wall surface facing the comparative resistance section and one of the end wall surfaces of the substrate, on the second surface of the substrate, and  
       (iii) at least one tubular passage within the flat substrate and which communicates between the recess wall surface that faces the comparative resistance section and one of the end wall surfaces of the substrate.  
     
     
       12. The flow rate detecting element according to  claim 11 , wherein the groove of the first fluid flow passage has a sectional area at an opening larger than sectional areas of any other portion of the groove. 
     
     
       13. The flow rate detecting element according to  claim 7 , wherein the first of the fluid flow passages includes the at least one tubular passage, and the second of the fluid flow passages is selected from the group consisting of 
       (i) a second hole which penetrates the thin film layer in the thickness direction so the fluid flows across the thin film layer on the upper surface and the lower surface,  
       (ii) at least one groove in the flat substrate and which communicates between the recess wall surface that faces the comparative resistance section and one of the end wall surfaces of the substrate, on the second surface of the substrate, and  
       (iii) at least one tubular passage within the flat substrate and which communicates between the recess wall surface that faces the comparative resistance section and one of the end wall surfaces of the substrate.  
     
     
       14. An assembly including an element holder accommodating a thermosensitive flow rate detecting element, wherein the thermosensitive flow rate detecting element comprises: 
       a flat substrate including a surface and end walls and having a thin film layer comprising an insulating support film and an insulating protective film laminated on the surface of the flat substrate;  
       a heating resistance section including a thermally sensitive resistor having a pattern and a comparative resistance section including a thermally sensitive resistor having a pattern, the heating resistance section and the comparative resistance section being disposed between the support film and the protective film of the thin film layer;  
       a recess which penetrates the flat substrate in a thickness direction and faces the comparative resistance section, and  
       at least two fluid flow passages through which the recess is in fluid communication with one of a surface of the thin film layer facing away from the recess and one of the end wall surfaces of the substrate, wherein the flow rate detecting element measures one of flow rate and velocity of the fluid, using the heating resistance section, according to fluid temperature sensed by the comparative resistance section; and  
       the element holder has a cross section with an airfoil shape and at least one gap opening in each of upstream and downstream portions with respect to the comparative resistance section.  
     
     
       15. The assembly according to  claim 14 , wherein a lower edge of the gap opening located upstream of the comparative resistance section is located at a position which corresponds to an upper surface of the flow rate detecting element accommodated in the holder. 
     
     
       16. The assembly according to  claim 14 , wherein a lower edge of the gap opening located upstream of the comparative resistance section is located at a position which corresponds to an end wall surface of the substrate of the flow rate detecting element that is accommodated in the holder. 
     
     
       17. The assembly according to  claim 14 , wherein a lower edge of the gap opening located upstream of the comparative resistance section is located at or below a lower surface of the substrate of the flow rate detecting element that is accommodated in the holder.